(1) Field of the Invention
This invention relates to an intra-field overlay alignment correction for a step and repeat exposure system, and more particularly to a method which provides an alignment correction prior to the exposure of each image field.
(2) Description of the Related Art
The use of Step and Repeat systems to expose patterns on integrated circuit wafers requires the use of both global or inter-field alignment and intra-field alignment. Most of the intra-field alignment schemes used make use of statistical data over a number of wafers to determine the correction parameters for a number of wafers, such as a production lot.
U.S. Pat. No. 5,444,538 to Pellegrini describes a method of determining correction parameters using least-squares analysis techniques of a number of wafers to determine the correction parameters for a number of wafers, such as a production lot.
U.S. Pat. No. 4,7685,883 to Waldo et al. describes a method of alignment using a reticle having an alignment mark positioned at the center of the reticle used to align each wafer in the stepper system as well as to adjust the stepper software.
U.S. Pat. No. 5,656,402 to Kasuga describes a method of determining alignment correction parameters using a method of reference to least squares in reference to the coordinates of each of the alignment marks and the coordinates of rational grid points.